1. Field of the Invention
The invention relates to a method and apparatus for drawing curved lines, particularly circles. More specifically the invention relates to a device which provides easy selection of desired curved line radius and which is easy for use to draw a near perfect curved line or circle having the selected radius.
2. Prior Art
Various drafting tools for drawing curved lines, arcs and circles are known in the drafting and design industries. A basic example is the compass. The typical compass is a V-shaped device having a pair of rigid arms connected at a hinge allowing the arms to be separated to any angle in a continuous span of adjustment. One of the arms carries a writing implement at the end, and the end of the other arm has a sharp point that pierces the writing surface to provide a central anchor or pivot about which the compass is rotated to draw an arc. If used properly, it is possible to draw a perfect circle using a compass. However, it is not always easy to do so. Frequently, the pointed arm is displaced from the pivot point while drawing. The separation of the arms sometimes can be changed inadvertently while drawing. These changes introduce imperfections in the drawn circle.
Accuracy of drawings is important. Accordingly, various devices are available to aid draftspersons to draw accurately, including devices for drawing curved lines and circles. U.S. Pat. No. 776,897--Ferris discloses a ruler having a pencil holding slide and a centering slide. Each slide is longitudinally adjustable along the length of the ruler. When used as a compass, a pin is depressed to engage and anchor the ruler to a paper surface. A writing device is inserted through an opening and engages the paper surface. The ruler can then be rotated about the pin for drawing arcs or circles of desired radii.
U.S. Pat. No. 893,085--Loughborough discloses a drafting instrument having a plurality of apertures for receiving a marking pen or pencil point. A moveable pin defines the point of rotation of the device, which is suited for use as a compass to draw circles.
U.S. Pat. No. 1,154,673--Van Ness discloses a drafting tool which combines the attributes of a T-square, triangle and protractor.
U.S. Pat. No. 1,327,154--Golden discloses a compass having a centering point and a bar. The bar extends radially from a disc. A longitudinal slot extending the length of the bar contains a slide which moves along the graduated surface of the bar. The slide has an enlargement with components for securing a piece of lead or the like. The lead can be rotated about the centering point to draw a circle of the desired size.
U.S. Pat. No. 1,402,629--Manly discloses a rule having a centering point and slot. A pencil carrier rides in the slot. A set screw secures the pencil carrier in position along the slot. Rotation of the device around the centering point produces a circle.
U.S. Pat. No. 1,808,705--Owen, Jr. discloses a combination compass, protractor and ruler. The device has a centering eyelet rotatably engaged in one end of a body. A plurality of openings are provided for receiving a pencil point or the like. In another embodiment, a slot carries a guide device. The guide device accepts a pencil point or the like and is slidable within the slot for drawing a circle or arc having the desired radius.
U.S. Pat. No. 1,825,266--Fischer discloses a combination ruler and compass having a pivot element and apertures for receiving a pencil point. In another embodiment, Fischer discloses a ruler and compass having a pivot element and a slide in a slot. The slot is adapted to receive a writing instrument.
U.S. Pat. No. 2,943,392--Attridge discloses a beam compass having a centering point and pencil carrier mounted on a track.
U.S. Pat. No. 3,460,261--Frey discloses a drafting device having a frame-like support member. An elongated, rotatable member is mounted within an opening of the support member. The rotatable member has an aperture for accepting a pencil point or the like. The rotatable member is rotated within the support member to draw circles or arcs of desired radii.
U.S. Pat. No. 3,465,445--Fischer discloses a drawing design apparatus which includes a plurality of concentrically arranged rings, each having a plurality of apertures for drawing circles having varying radii.
U.S. Pat. No. 4,129,948--Hatter et al discloses a circle drawing device having a flat circular disk having a hardened steel center pin. The disk has a plurality of holes for accepting a drafting instrument. The entire disk rotates about the center pin to draw circles.
U.S. Pat. No. 4,530,156--Kettlestrings discloses a rotatable disk for drawing circles. Kettlestrings discloses a non-concentric rotatable disk located within a first rotatable disk. The non-concentric rotatable disk is rotated to a desired point to provide a circle of desired radius. The non-concentric rotatable disk can be locked into place while the first rotatable disk is rotated about a center to draw the circle.
U.S. Pat. No. 4,125,161--Guthrie discloses a circle drafting instrument having a slotted disk rotating within a support member. The slotted disk has a plurality of slots, each having a plurality of wedge shaped notches for placement of the point of a drawing instrument.
These and other prior art disclosures show that rotating disks having apertures for accepting the point of a pencil or the like are known as a means for drawing curved lines or circles. The disks function in lieu of the pivotable legs of the V-shaped compass or the fixed distance between the pivot point and pencil apertures of an elongated rule, to locate the pencil point at a set distance from the pivot point for drawing a curved line or circle. Typically, the user chooses among fixed pencil apertures at different radii, however slide mechanisms that are movable to set the pencil or other drawing instrument at a desired radius also are known.
Rotatable disks having a plurality of fixed holes for accepting the point of a writing instrument do not permit an inadvertent change in radius during drawing, and generally provide near perfect curved lines and circles. However, it is only possible to draw a circle at one of the discrete intervals defined by the fixed holes. It is possible to provide many holes at different radii, but such holes cannot span the entire radius. The sliding structure precludes holes, for example, close to the junctions between the rings.
A device such as an elongated ruler having a slide mechanism, for positioning a pencil point at any desired radius within an adjustment range, enables more precise selection of the circle radius. However, the device is subject to the same dislocations as a compass, such as dislocation of the pivot point from the paper and consequent imperfection of the drawn circle.
It would be desirable to provide a device for drawing curved lines or circles that can make near perfect circles like a rotating disk type drafting tool, and also has means to select a desired radius within a range of adjustment as provided by the sliding pencil aperture type drafting tool. Such a device according to the present invention has the adjustment advantages of a compass and the fixed center and radius advantages of a rotating disk guide.